Pip recording apparatus

ABSTRACT

This disclosure comprises the recording and/or storing of information received in the form of electrical signals by scanning and illuminating at least a portion of the surface of a PIP material with a constant intensity radiation beam and applying a varying potential to the illuminated surface in accordance with the electrical signals so as to selectively polarize the PIP material. PIP material is used herein is defined as any material capable of exhibiting &#39;&#39;&#39;&#39;persistent internal polarization&#39;&#39;&#39;&#39; under the influence of radiation and an applied electric potential.

United States Patent Rosenberg et al.

[54] PIP RECORDING APPARATUS [72] Inventors: Barnett Rosenberg, Lansing; Felix H. Brown, Okemos, both of Mich.; David Theodore Nelson Williamson, London; Walter H. Bossons, Saunderton, both of England [731 Assignees: Molins Limited, London, England by said Williamson and said Bossons; Owens-Illinois, Toledo, Ohio by said Rosenberg and said Brown, part interest to each [22] Filed: Mar. 7, 1967 211 Appl. No.: 621,205

[52] US. Cl. ...178/6.6 A, 346/74 P, 355/3 [5 1] Int. Cl ..H04n 5/80, 003g 15/00 [58] Field of Search ..346/l 74 P; 96/1; 178/6.6 A; 355/3; 340/173 LS [56] References Cited UNITED STATES PATENTS 3,199,086 8/1965 Kallmann et a] ..340/ 173 [4 Feb. 15, 1972 3,308,233 3/1967 Button et al. ..l78/6.6 3,396,235 8/1968 Button et al. .....l78/6.6 3,337,339 8/1967 Snelling ..96/l

Primary Examiner-Joseph W. l'lartary At!0rneyD. K. Wedding and W. A. Schaich [57] ABSTRACT This disclosure comprises the recording and/or storing of information received in the fonn of electrical signals by scanning and illuminating at least a portion of the surface of a PIP material with aconstant intensity radiation beam and applying a varying potential to the illuminated surface in accordance with the electrical signals so as to selectively polarize the PIP material.

PIP material is used herein is defined as any material capable of exhibiting persistent internal polarization" under the influence of radiation and an applied electric potential.

5 Claims, 6 Drawing Figures PIP RECORDING APPARATUS DISCLOSURE OF THE INVENTION This invention relates to a novel process and apparatus which utilize the principles of persistent internal polarization for recording, storing, and/or subsequently reproducing information received in the form of electrical signals.

Persistent internal polarization (abbreviated herein as PIP) involves the separation of positive and negative charges in a photoconductive insulating material by simultaneous irradiation and the application of an electric field. The charges are subsequently trapped and remain fixed or frozen in the photoconductor for a finite time to form an internal polarization field. This process and the theory thereof are well known in the art. See, for example, Electrophotography by R. M. Schaeffert, The Focal Press, London and New York (I965), pages 59-77, and Persistent Internal Polarization by Kallmann and Rosenberg, The Physical Review, Vol. 97, No. 5, (Mar. 15, 1955), pages 1596-l6l0, both of which are incorporated herein by reference.

Thus, as used herein, photoconductive insulating material is defined as any material capable of acquiring persistent internal polarization under the influence of radiation and an electric field. For convenience, such materials will be referred to hereinafter as PIP materials.

As noted hereinbefore, the relevant characteristic of the PIP material is that, when subjected to illumination simultaneously with the application of an electric field, so-called photoelectrets are created within the material which thereafter behaves as if it carried an electrostatic charge just below an insulating surface, in which state it is said to be polarized. Further illumination of the material with or without a simultaneous application of an electric field of reverse polarity, returns the material to its original state.

It is possible to polarize PIP material by first illuminating it and subsequently applying an electric field. However, for any given illumination and field strength, the degree of polarization produced is greatest when the field is applied simultaneously with illumination and becomes progressively less as the application of the electric field is more delayed after illumination. The illumination may be regarded as serving to sensitize the material to the field, and the sensitivity decays progressively after illumination ceases, the rate of decay being different for different materials.

In accordance with this invention, there is provided a process for recording and/or storing information received in the form of electrical or equivalent signals which comprises scanning and illuminating at least a portion of the surface ofa PIP material with a radiation beam, subjecting the illuminated surface to an applied potential, and varying the applied potential in accordance with the received signals so as to selectively polarize the PIP material.

In the further practice of this invention, it is contemplated reproducing, e.g., by an electrostatic copying technique, the information which has been recorded and stored by selective polarization of the PIP material.

It is contemplated that the PIP material may be mounted on any suitable base which has sufficient electrical conductivity to serve as an electrode. Immediately adjacent to the external surface of the PIP material there is positioned a further electrode such that when a potential difference is established between the external electrode and the base, the PIP material is subjected to the influence ofan electric field.

According to one embodiment of this invention, we provide a process and apparatus for recording and/r storing information received in the form of electrical signals, which comprises a movable, preferably rotatable, member having an exterior surface layer of PIP material backed by an electrically conductive support, at least one electrode being positioned adjacent to said surface, voltage-applying means connected to establish a potential difference between the electrode and the support so as to create an electric field through the surface, the electrode extending across the surface so that the resulting field is effective at any instant over a zone of the surface, means for moving the member so that the whole of the PIP surface passes through said field in successive zones, optical means arranged to produce a light beam and to deflect said beam cyclically along a portion of the zone subject to the electric field so as to scan said portion in synchronism 'with the operation of the moving means, and means for applying the received signals to the voltage-applying means so as to vary the electric field in accordance with said signals.

Preferably the movable member is a rotatable drum and the electrode is an elongated member extending substantially parallel to the axis of the drum such that the zone of the drums surface subject to the electric field at any instant is an elongated strip; the electrode may however conveniently be arranged with a slight angle of skew so that the strip of the drums surface which is scanned during any one traverse of the light beam will in fact be parallel to the drum's axis in spite of the rotation of the drum during that traverse.

The PIP material when subjected to illumination simultaneously with the application of an electric field is polarized to an extent which is a function of both light intensity and the applied potential. Thus in apparatus embodying the invention as defined hereinbefore, whenever a constant intensity light beam moves along a zone of the surface, any particular area of the surface will be polarized to an extent dependent uponthe applied potential while the beam illuminates that area.

It is known in the art that the light intensity may be varied and the electric field held constant, but this has the disadvantage of limiting the maximum speed of scanning due to the relatively slow response of most devices for control of light intensity. In accordance with this invention, such prior art limitation is substantially avoided by varying the field while holding the light intensity constant. It is further contemplated herein that both the electric field and light intensity may be varied; for example, where the control signals require both long-term (low-frequency) and short-term (high-frequency) variations of the resultant polarization, the light intensity may be subjected to the long-term variations. I

The polarization produced in the PIP material of the drum or other rotatable member contains, as varying degrees of polarization, a representation of the image desired to be printed. The form of such representation depends of course upon the form of the control signals, e.g., if the latter contains voltages representing a continuous range of tones as in a television signal the PIP material will contain a continuous range of degrees of polarization, while if the signals represent a half-tone picture, i.e., switch between two defined levels, then the polarization will appear in a similar pattern.

It has been noted above that the sensitivity of PIP material to an electric field is greatest (for any given illumination level) where the field is applied simultaneously with the illumination, and decays progressively after illumination ceases. Accordingly, in the process and apparatus of the present invention, although the maximum polarization of the PIP material produced by the applied potential at any instant is to be found in the area illuminated at that instant, a smaller degree of polarization is also found in areas scanned immediately prior to that instant. While this effect is undesired and degrades the polarization image produced in the material, it can however be minimized by careful control of the level of illumination and range of applied potential, having regard to the speed of scan and, of course, the characteristics of the specific PIP material employed.

Printing if desired may be completed in any convenient manner, for example, using methods and materials employed in Xerographic or other electrostatic copying machines. In one embodiment contemplated herein, after each zone of the rotatable member has passed the electrode, it passes a reservoir containing ink e.g., particulate or colloidal ink of such potential as to be attracted to the polarized areas of the PIP material. After passing said reservoir, each strip passes adjacent to (or briefly into contact with) a travelling web of paper or other desired substrate material and the ink carried Thus, in the practice of this invention, the technique of such electrostatic printing or copying may be used in conjunction with a scanning technique (in principle analogous to that employed in television) to provide a printing apparatus which will operate so as to produce printed images whose form is defined by electric signals received by the apparatus. Such signals may be similar in origin and form to television video signals or may take other forms, e.g., may be character-representing code signals emitted by an electronic computer.

In the further practice of this invention, it is contemplated that the PIP material which is mounted on an electrode base may be peelable or otherwise physically removable from the base such that the PIP material (polarized in accordance with the received information) may be appropriately stored until printout or other feedback is desired.

Typical PIP materials contemplated in the practice of this invention include not by way of limitation both organic and inorganic materials such as zinc sulfide, cadmium sulfide, zinc selenide, cadmium selenide, zinc oxide, cadmium oxide, selenium, tellurium, anthracene, chrysene, alkaline earth halides, and mixtures of same, especially mixtures of selenium with tellurium, zinc-cadmium selenides, and zinc-cadmium sulfides. It is also contemplated that a small effective amount of a suitable activator, e.g., gold, silver, or copper, may be incorporated with the photoconducting PIP substance.

The commonly used powdered PIP materials are typically dispersed or mixed with a suitable resin binder such as a cellulose acetate, ether, or ester, silicones, vinyl resins, and/or epoxy resins.

The term radiation" as used herein is intended to include any form of electromagnetic radiation or energy, visible or invisible, which will cause photoconductive insulator PIP material to become conductive so as to acquire an electric charge in an electric field. Such radiation includes not by way of limitation visible light, infrared, ultraviolet, X-rays, gamma rays, and beta rays.

THE DRAWING In order that the invention may be better understood, a preferred embodiment thereof will now be described, with reference to the accompanying diagrammatic drawings in which:

FIG. I is a general schematic diagram of a printing apparatus embodying the invention;

FIGS. 2, 3 and 4 are views of part ofthe apparatus of FIG. 1, to a larger scale and in end view (partly in section), side elevation, and plan respectively; and

FIGS. and 6 are fragmentary views showing other embodiments of FIG. 1.

Referring first to FIG. 1, electric control signals of similar form to television video signals (which may merely alternate between two levels representing black and white e.g., if a halftone picture is to be printed) enter on a line 1 and first pass through a sync separator 2 which has two outputs; the first output delivers synchronizing signals on a line 3 while luminance signals are delivered by the second output on a line 4. The synchronizing signals travel via an amplifier 5 to a drive unit 6 which rotates a mirror drum 7 under control of said signals. The luminance signals go to a wide-band amplifier 8 delivering a voltage output (including a DC bias component if required) to a pair of lines 9, 10 connected respectively to a rotatable drum 11 and a field electrode 12 mounted above and close to said drum.

The drum 11 comprises an electrically conductive core 11a supporting an outer coating 11!; of PIP material (FIG. 2). The

field electrode 12 is an elongated fiat plate with a longitudinally extending central slot 13 and is mounted close to the drum 1], in a plane parallel to a horizontal plane containing the axis of said drum. The slot 13 extends very nearly parallel to said axis, being skewed at a slight angle 5 (FIG. 4) for a reason to be explained.

A lamp l4 energized by DC and an optical system 15 (represented as a single lens) direct a light beam 16 on to mirror drum 7, whence said beam is reflected through slot 13 of field electrode 12 on to the surface of drum 1]. The light beam 16 is focused by optical system I5 to produce a small area or spot" of illumination on the surface of drum II, but as the mirror drum is rotated this spot scans or travels along slot 13, moving from right to left as seen in FIG. 3. As the spot reaches the left-hand end of the slot 13, however, it vanishes and reappears at the right-hand end of said slot to commence another traverse. This spot movement arises because mirror drum 7 is of the known type comprising a series of plane mirrors secured to a common support so that the assembly of mirrors in section or end view appears as a regular polygon (FIG. 3). Whenever the field electrode 12 is at a potential other than zero (relative to the core 11a), that area of coating 1 lb then illuminated by the spot is polarized.

The drum 11 and mirror drum 7 are both rotated during operation of the apparatus, the drive (not shown) to drum 11 being either taken from the same drive unit 6 or otherwise synchronized with the drive to mirror drum 7 so that the speeds of the two drums are maintained in constant ratio.

After any point on the drum 11 has passed the field electrode 12, it next passes a so-called developing station 17, which essentially comprises a reservoir for ink (sometimes termed toner). The ink in said reservoir is electrically charged, with polarity opposite to that of the persistent internal polarization or trapped charge produced in the drum coating 11b (near its external surface) by the simultaneous action of the light beam and the electric field between the field electrode l2 and the core 11a, and accordingly whenever a polarized area of the drum coating Ilb passes the station 17, ink travels to that area of the surface of the drum in quantity determined by the degree of polarization. Thereafter continued rotation of the drum 11 brings the area of the drum being considered, carrying the transferred ink, to the lowest part of the drum and here a web 18 of paper travels horizontally under, and closely adjacent to, the drum 11 but above a transfer electrode 19. The web 18 travels at a linear speed equal to the peripheral speed of the drum 1] and in a direction normal to the vertical plane containing the axis of the drum 1 1.

Transfer electrode 19 is connected by line 20 to a supply terminal 21 which in turn is connected to an external DC source by which the electrode 19 is maintained at such a potential and polarity, relative to the core of drum II, that the electric field established between drum 11 and electrode 19 causes the ink carried by the drum 11 to transfer to the paper web; the ink then remains on and travels with the web past a so-called fixing station 22 where treatment (e.g., heating) according to the nature of the ink is applied to the web and ink to bond the ink to the web.

After the ink has thus been removed from the drum 11, the area of the drum which has been considered passes a cleaning station 23 before again arriving at the position under field electrode 12 for a further cycle of use. In cleaning station 23, any convenient drum cleaning devices such as rotary brushes, suction devices, and further electrodes at ink-attracting potential may be provided to ensure that any residual ink is removed from the drum and it is preferred also at this position to provide for subjecting the coating lIb simultaneously to illumination and an electric field of such polarity as to bring the coating 11b to a condition of uniform polarization, either substantially zero or of opposite polarity to that liable to be produced on passing the field electrode 12.

Reverting to the action of the light beam 16 in conjunction with the varying applied potential created by the varying potential on field electrode 12, with a constant light intensity it will be understood that each traverse of the scanning light beam from end to end of the drum 1] results in a strip of the coating of the drum being polarized, the degree of polarization of any small area of the strip being dependent upon the potential of electrode 12 while the light beam fell upon that point. In other words, where there is no potential, there is no resulting polarization.

Thus, from the hereinbefore description, it will be understood that the building up of an image in the form of a pattern of varying polarization of the coating 11b is analogous to the buildup of a television picture in a cathode-ray tube, save that the light beam here only moves in one dimension of the surface on which the image is formed, the surface itself being moved in the second dimension. However, it is not intended that the invention be per se limited to a rotating drum; that is, a flat, planar structure may be employed in lieu of a drum with appropriate changes of electrode structure, for example, a transparent tin oxide coated electrode which substantially covers the entire planar structure and exposes the entire surface thereof to the electric signals.

As the surface movement i.e., drum rotation) is continuous, if the slot 13 of field electrode 12 were parallel to the drum axis then the strips of surface covered by successive scans would necessarily be skewed on the drum. To avoid this effect, which would necessarily have to be allowed for in the control signals supplied, i.e., so that said strips are parallel to the drum axis, the slot 13 is itself skewed at the angle S (FIG. 4), said angle being readily calculated from the peripheral speed of the drum and the speed of traverse of the light beam, as it will be apparent that the sine of this angle S equals the peripheral speed of the drum divided by the speed of traverse of the light beam along the slot 13; this relationship is of course stated on the assumption that the drum peripheral speed is low comared with the beam traverse speed, so that the beam need not travel so far from the vertical plane through the drum axis that the curvature of the drum cannot be ignored.

FIGS. 5 and 6 illustrate two alternative forms of the -field electrode. That of FIG. 5 is generally similar to the electrode 12 of FIGS. 1-4, but portion 12a of the plate on either side of the slot 13 is inclined the edges 12b defining the slot 13 being knife-edges. With this arrangement the electric field between the field electrode and the drum is more localized than with the flat plate 12 ofFlGS. 1-4.

In HO. 6, the field electrode is in the form ofa half-cylindrical glass rod 120, arranged with its curved face 12d towards the drum 11. The said face 12d is coated with a transparent or translucent electrically conductive material, e.g., tin oxide. With this form of field electrode, the electric field is again more localized than when using the flat slotted plate 12 of FIGS. 1-4. The glass rod 12c will of course function as a plane-convex lens, causing the light beam 16 to converge, and allowance for this must be made in the design of the optical system 15.

In lieu of tin oxide coated glass, there may be used a strip of transparent film (e.g., of synthetic material such as polyvinyl acetate, polyethylene, or Mylar) having on its lower face a coating of transparent or translucent electrically conductive material such as aluminum or gold.

Apparatus embodying the invention may be arranged for control by signals of various forms. As above described the form of control signal required is that of a television video signal and the apparatus could usefully be applied to facsimile systems, given acompatible transmitter. In another application, such apparatus could be used for printing under control of output signals from an electronic computer. In this instance the exact form of control signals available (and hence of input circuits to the apparatus) depends upon the basic coding used in the computer, e.g., binary, binary-coded decimal, biquinary, and whether the computer operates on a serial or parallel basis. However, in such a use the characters to be printed can conveniently be provided as stencils or transparencies on a rotatable drum or disc through part of which the light beam 16 passes, the optical system being so arranged as to focus an image of the characters represented on such character drum or disc, one at a time, on the surface of drum 1] (the slot 13 being made wide enough to accommodate character images of desired size). The rotation of the character drum would be synchronized with the incoming control signals, and rotate so fast as to permit all available character images to appear on the surface of drum 11 in such a short time that the movement of beam 16 is negligible (relative to the character image size). Normally the field electrode 12 would be kept at zero potential relative to drum core 11a, but during the period when each area of the drum 11 which is to receive a character is illuminated the control signals would produce a voltage pulse on said electrode while a desired character image is present on the surface of drum 1], so that the coating 11b is polarized in a pattern correspondingto the form of such desired character image.'

We claim:

1. Apparatus for recording information received in the form of electric signals, which apparatus comprises a movable member having an exterior surface formed by a layer of PIP material, said PIP material being capable of selective polarization internally throughout the subsurface of the photoconductive layer, an electrically conductive support backing said layer, at least one electrode positioned adjacent to said surface, voltage-applying means connected to establish a potential difference between the electrode and the, support so as to create an electric field through said surface, the electrode extending across the surface so that such electric field is at any instant effective over a zone of said surface, means for moving the member so that the whole of said surface passes through said field in successive zones, optical means arranged to produce a light beam and to deflect said beam cyclically along a portion of the zone subject to the electric field so as to scan said portion in synchronism with the operation of the moving means, said field electrode comprising an elongated member with a longitudinally extending slot and said. optical means being arranged to direct the light beam through said slot'and to deflect said beam cyclically along said slot, and means for applying the received signals to the voltage-applying means so as to vary the electric field in accordance with said signals.

2. Apparatus as claimed in claim 1, in which the movable member is a rotatable member.

3. Apparatus as claimed in claim 1, in which the optical means includes a mirror drum, said mirror drum comprising a series of plane mirrors and a common support, the plane mirrors being secured to the common support in such manner that the assembly in section or end view appears as a regular polygon.

4. Apparatus as claimed in claim 1, in which the movable member is a rotatable drum and the field electrode is disposed at a slight angle of skew to the axis of said drum, said angle being so related to the ratio of the speed of the drum and the speed of deflection of the light beam so that the successively scanned portions of the surface are parallel to said axis.

5. Apparatus as claimedin claim 4, including an ink reservoir adjacent to the surface of said drum, means for maintaining said reservoir, and hence ink therein, at a potential such that said ink is attracted to polarized areas of the surface of the drum, means for causing a continuous web of substrate material such as paper to pass through a transfer zone in which said web is in juxtaposition to the surface 'of the drum at a velocity equal to the peripheral velocity of said drum, means for applying an electric field to cause transfer of ink from the drum to the web, and cleaning means for the drum surface, the relative dispositions of the elements being such that upon rotation of the drum any point on the drum surface passes, in order, the field electrode, the ink reservoir, the transfer zone, and the cleaning means. 

1. Apparatus for recording information received in the form of electric signals, which apparatus comprises a movable member having an exteRior surface formed by a layer of PIP material, said PIP material being capable of selective polarization internally throughout the subsurface of the photoconductive layer, an electrically conductive support backing said layer, at least one electrode positioned adjacent to said surface, voltageapplying means connected to establish a potential difference between the electrode and the support so as to create an electric field through said surface, the electrode extending across the surface so that such electric field is at any instant effective over a zone of said surface, means for moving the member so that the whole of said surface passes through said field in successive zones, optical means arranged to produce a light beam and to deflect said beam cyclically along a portion of the zone subject to the electric field so as to scan said portion in synchronism with the operation of the moving means, said field electrode comprising an elongated member with a longitudinally extending slot and said optical means being arranged to direct the light beam through said slot and to deflect said beam cyclically along said slot, and means for applying the received signals to the voltage-applying means so as to vary the electric field in accordance with said signals.
 2. Apparatus as claimed in claim 1, in which the movable member is a rotatable member.
 3. Apparatus as claimed in claim 1, in which the optical means includes a mirror drum, said mirror drum comprising a series of plane mirrors and a common support, the plane mirrors being secured to the common support in such manner that the assembly in section or end view appears as a regular polygon.
 4. Apparatus as claimed in claim 1, in which the movable member is a rotatable drum and the field electrode is disposed at a slight angle of skew to the axis of said drum, said angle being so related to the ratio of the speed of the drum and the speed of deflection of the light beam so that the successively scanned portions of the surface are parallel to said axis.
 5. Apparatus as claimed in claim 4, including an ink reservoir adjacent to the surface of said drum, means for maintaining said reservoir, and hence ink therein, at a potential such that said ink is attracted to polarized areas of the surface of the drum, means for causing a continuous web of substrate material such as paper to pass through a transfer zone in which said web is in juxtaposition to the surface of the drum at a velocity equal to the peripheral velocity of said drum, means for applying an electric field to cause transfer of ink from the drum to the web, and cleaning means for the drum surface, the relative dispositions of the elements being such that upon rotation of the drum any point on the drum surface passes, in order, the field electrode, the ink reservoir, the transfer zone, and the cleaning means. 